In the field of glass melting, there has been an increasing awareness of the necessity to control the pollutant levels of emissions. This awareness has been heightened by the increasing number and severity of regulations governing these emissions. In these regulations a comparison is made between pollutant levels of input gas and compared to those of output gas released into the atmosphere. The process itself is treated as a "black box" system between those input and output values.
For example, United Kingdom patent application number GB2243674 utilises infra-sound on a vertically moving heated air sUream into which powdered glass batch has been introduced. Infra-sound has a frequency of less than about 20 Hertz. The infra-sound vibrates the heated air stream and effects heat Transfer from the air stream to the glass batch particles so that the glass batch particles are heated and the temperature of the heated air stream is reduced to a temperature below 700.degree. C. This reduces the propensity of the air to produce NOx. Fuel is subsequently added as the heated glass batch particles and the cooled air stream move downwardly towards the crown of the furnace. The waste gas from the process is used regeneratively in a heat exchanger to effect heating of the initial air stream.
However, it is still desirable to reduce the level of pollutants emitted from the furnace relative to the levels in the ambient air drawn into the furnace (which is the standard used in the regulations referred to above).
A method has been devised to operate such a furnace which is applicable to industrial furnaces generally.